Electricity meters, or simply meters, are devices, that among other things, measure electrical energy consumed by a residence, factory, commercial establishment or other such facility. Electrical utilities rely on meters for many purposes, including billing customers and tracking demand for electrical power. A common form of meter utilizes current transformers to sense the electrical current being supplied to the facility being metered. The current sensed by the current transformers is transmitted to circuit boards included in the meter to facilitate measurement of the amount of electrical energy being consumed by the facility.
A typical electricity meter includes several electrical components, ranging in size from relatively large power busses and transformers to microelectronic devices. Because of the variety of components within meters, labor and cost associated with assembling electricity meters can be a limiting factor in cost of electricity meters.
For example, electricity meters require heavy duty, thick copper current blades that are received by the meter housing to allow the meter to be coupled to the electrical power lines. These blades must in turn be connected to conductors, called current coils, that provide current signals to a current transformer within the meter. Moreover, voltage measurements are typically obtained from the current coils, thereby requiring connection to yet another, thinner lead wire that is also connected to a circuit board where the digital processing circuit is located. All of the various interconnections, for example, between the blade and the current coil, require complex bolt terminals or solder connections, which are labor intensive.
Another source of cost arises from the need to isolate the current transformers in electricity meters. As discussed above, electricity meters typically include one or more transformers that obtain low level current signals representative of the current flowing through the current coil. These low level current signals, combined with voltage measurements, allow for the power calculations to take place. The current transformers are typically in the form of a toroid, with the current coil passing through the center opening or void. A toroid, as is known in the art, is a circular or rounded core wrapped by a copper wire coil. Because the current transformer includes the bare wire coil, and is disposed in close proximity to the high voltage and current on the current coil, it is necessary to provide an insulation cover to inhibit dangerous arcing between the current coil and the current transformer wire coil.
In prior systems, the entire current transformer was coated with a heated, liquid, thermoplastic resin that cooled and hardened to form an insulation layer. In some cases, the current transformer was seated in a plastic insulating shell, and the thermoplastic resin was used to close off the shell. It has been found, however, that the use of the thermoplastic resin can be inconvenient and time consuming.
Accordingly, there exists a need for a method of providing an insulating cover for a current transformer that avoids one or more of the problems of the prior art discussed above, as well as others.
Moreover, as discussed above, the current coils of electricity meters typically carry a high voltage and/or high current. Such current coils are typically in the form of a bare copper wire or bare copper bar. If the current coils from different potentials of the power line are disposed too close to one another, a risk of arcing between two current coils may arise.
The nominal way to prevent such arcing consists of maintaining a significant minimum distance between the current coils. While maintaining distance between coils inhibits arcing, it often is not practical or cost effective. For example, it is possible in some cases to measure current from two different current coils using the same current transformer. However, passing both current coils within the same current transformer necessarily places the current coils within close proximity of each other.
As a consequence, there is a need for a more effective method of reducing the possibility of arcing between high voltage and/or high current carrying conductors in electricity meters.